This is a utility application with priority based on Prior Foreign Application number GB 0119318.4 filed Aug. 8, 2001 which relates to Priority Data Ref GB 0105706.6 filed Mar. 7, 2001.
This invention is supported by a U.K. Government xe2x80x9cSmart Awardxe2x80x9d Feasibility Study Ref. number 1007, with financial support from the Department of Trade and industry for the research and development of a working prototype. The U.K. Government has placed certain restrictions on the manufacture of this invention.
The technical field of the invention relates to the design of disc-shaped aircraft with the capability of vertical take-off and landing, including hovering capability as well as fast forward flight.
The conventional helicopter""s forward horizontal speed limit is due to unequal lift forces acting on the forward and retreating rotor-blades as speed increases: the invention disclosed overcomes this problem by using contra-rotating propellers which deliver thrust required for VTOL flight, in conjunction with a separate engine for horizontal thrust. The propellers are enclosed inside an annular chamber that has an air intake at the top, and an annular vent below, so that following the transition to horizontal flight, the propeller intake shutters can be closed allowing free airflow over the aerodynamic shape of the disc, and this provides the lift required for high-speed horizontal flight. With the propellers enclosed inside a chamber within the aircraft the present invention exhibits a notable safety feature by eliminating the risk of the propeller blades striking a person or an external object. Whereas conventional helicopter rotor-blades can crack and fall under severe stress of impact, causing catastrophic loss of the aircraft, the invention disclosed uses propellers that are inherently stronger than rotor-blades and have a smaller rotation-disc diameter for a given thrust performance. Existing helicopter rotor systems require complicated transmission gearing between the engine and rotor-shaft, together with complicated mechanisms that change the angle of attack of forward and retreating rotor-blades on every rotation, as well as controls to change both cyclic and collective pitch of the rotor disc. The present invention removes all the complex mechanism of the helicopter by providing a central vertically mounted engine with direct drive to the prop-shaft via a contra-rotating co-axial gearbox: it is therefore safer to fly and less expensive to maintain than a helicopter. A further safety feature allows for the auto-rotation of the propellers in event of engine failure, so that the pilot can effect an emergency landing with the aid of vectored down-thrust from the separate horizontal engine.
Preceding designs of circular plan-form aircraft such as the Avro VZ-9-Avrocar featured heavy turbo-fan engines situated laterally around a central fan that dissipated thrust to vents around the circumference of the aircraft to achieve both lift and horizontal thrust; but the available thrust was unable to achieve vertical take-off and un-countered torque forces resulted in instability. Similarly, recent designs for unmanned aerial vehicles using rotor systems driven by engines positioned laterally within an annular fuselage, dissipate the airflow below the rotor. In the invention disclosed, a light-weight turbine mounted vertically drives contra-rotating propellers that provide equilibrium and stability; and the airflow from the propellers is forced downward and outward through an annular funnel-shaped chamber. Aerodynamic control vanes situated in this pressurised airflow control the pitch, roll and yaw axis of the aircraft, together with aerofoils which provide additional lift forces. Previous disc-shaped designs have experienced a nose-up pitching moment in forward flight however: in the present design disclosed, this tendency to pitch-up is countered by the concave shape of the underside rim of the aircraft, (proved in wind-tunnel tests at Cranfield University U.K.), and by downward-vectored thrust from the horizontal jet engine. Recent wind-tunnel tests have also confirmed that the lenticular shape of the aircraft disclosed has a very high lift-to-draft ratio. Using this aerodynamic disc-shape with a horizontal thrust engine that can be steered through 360 degrees, the aircraft disclosed can fly and manoeuvre in any direction.
The invention comprises a circular VTOL aircraft which is capable of vertical and horizontal flight by combining propulsive power from horizontal contra-rotating propellers powered by a turboprop engine giving vertical thrust, and a jet turbine engine or engines, giving horizontal thrust. The stability of the aircraft is achieved by the gyroscopic effect of the high-speed rotation of two co-axial propellers, which can be geared to contra-rotate at the same speed thus avoiding the torque effect produced by a single rotor or propeller.
The jet engine (or engines), that provides horizontal thrust, is mounted on a steerable turntable pod at the centre-base of the aircraft in order to achieve rapid changes in direction through 360 degrees during flight manoeuvres: for example, from forward to reverse flight, from forward to sideways flight through 90 degrees, or from side-to-side flight through 180 degrees change in direction. The jet turbine may be fitted with vectored thrust nozzles to provide additional thrust on take-off. Alternatively, the turbine may be mounted on a gimbal bearing so that the engine can be angled upwards from the horizontal axis to provide additional take-off thrust.
This rapid manoeuvrability in the horizontal plane combined with a high rate of ascent or descent in the vertical plane, together with inherent stability as a weapons or personnel recovery platform, is designed to make the aircraft extremely effective for both military application and for civilian rescue operations: particularly rescue from fire in high-rise buildings or cliff-face rescue operations. A circular passenger compartment, as well as payload, fuel tanks and weapon bays may be incorporated in the main circular body of the aircraft. For the military application the passenger compartment area may be used both for weapons payload and for additional fuel tanks in order to extend the normal operating range. Weapons can be arranged to give 360 degrees of effective fire cover.
The aircraft is to be constructed using composite GRP and carbon-fibre reinforced materials, which are both strong and light in weight, and will enable the aircraft to exhibit a low radar profile. A feature of the design is the high fuel storage capacity, with fuel tanks installed around the circumference of the craft to make full use of the large outer area available; this high fuel capacity will enable the aircraft to out-range the conventional helicopter on passenger flights and rescue or military missions.
Another notable feature of the design is that the passenger compartment, cargo and fuel-tank areas are all integrated into the main body of the craft, which combines the functions of both wing and fuselage in one inherently strong disc-shape aerodynamically streamlined to generate lift in forward flight, thus avoiding existing problems such as wing-flutter and spar-failure associated with high loading on conventional aircraft designs. The circular passenger compartment can be designed either to maximise seating capacity of to include a small service area. (For example, the prototype aircraft is 12 metres in diameter and is designed to carry 24 passengers and 2 flight crew, with a fuel capacity of 33 cubic metres). The area designated for the passenger compartment may also be used for cargo carrying purposes. Alternatively, with the passenger compartment area replaced by water or foam tanks the craft can be used effectively as a fire-fighter having the ability to lift and dump a large quantity of water/foam from the circular tanks on each mission. The flight-deck is completely separate from the passenger compartment and is therefore inaccessible to high-jacking attempts.
The horizontal speed of the aircraft described is not limited by aerodynamic problems caused, by the difference in forward and retreating blade speeds of the helicopter rotor, because, in horizontal flight with the rotor intake-cover closed, the aerodynamic section of the disc-shaped aircraft produces an area of low pressure airflow over the trailing top half of the disc, generating lift in the same way as a conventional aircraft wing in forward flight. With the rotor intake-cover closed, the contra-rotating propellers are free to rotate at reduced cruising rpm sufficient to provide the gyroscopic stability required for horizontal flight; at the same time the rotor-chamber becomes partially vacated as air is expelled from the exit vent, allowing the propellers to rotate with reduced air friction, thereby conserving fuel for the turboprop""s main purpose of vertical take-off and landing.
In the event of engine failure the contra-rotating propellers may be geared to auto-rotate to control the rate of descent of the aircraft for an emergency landing. The horizontal jet thrust may also be vectored downwards by vectored thrust nozzles, or by extending a flap from the underside of the aircraft to deflect thrust to cushion the landing, or when the jet engine is gimbal mounted, thrust can be angled downwards to control the rate of descent. In the event of the horizontal jet turbine engine failing, an emergency landing can be made with the controlled thrust of the turboprop engine and propellers.
The aircraft is designed to fly with the main disc-shaped body maintaining a level horizontal position through all stages of flight, thereby alleviating passenger discomfort experienced during pitch and bank changes in conventional aircraft. However, the aircraft is fitted with control vanes that are used to change or trim the pitch and roll movement of the disc in flight. A combination of thrust from both vertical and horizontal power units will achieve a 45 degree angle of ascent to cruising altitude with the aircraft maintaining a horizontal altitude. The landing approach can vary from vertical to 45 degrees, thus significantly reducing noise levels around major airports. Vertical ascent from a helicopter pad or small clearing area can be made using the vertical thrust power unit alone.